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Tech feature: May 1, 2009

Training: Do you need that kind of pressure?

If you're looking to squeeze a little extra performance from your body, it's
likely you've already come across compression garments. The many studies into
their benefits have drawn wildly different conclusions, so Cycling Plus'
Nick Morgan finds out what's solid fact and what's still unproven.

The theory

The main point of compression garments is to apply pressure to the body and
thus improve your blood's circulation. Specifically, it's claimed that compression
garments increase the flow of de-oxygenated (venous) blood back to the heart.

This doesn't improve performance directly, but some scientists believe the
increased flow of blood may cause the heart's muscles to stretch to accommodate
the extra returned blood, which should result in increased output.

Dual benefit?

Unfortunately, as simple as the theory is to grasp, it's equally hard to prove.
Elements of it are well established, though. For example, a study at the Royal
Free Hospital in London found evidence compression stockings did indeed increase
blood return to the heart, but didn't investigate if this had a knock-on effect
on cardiac output.

Elsewhere, researchers from Osaka City University found some evidence of improvement
in cardiac output from wearing compression stockings, but their conclusions
must be treated cautiously for two reasons. Firstly, they measured cardiac output
at rest. Secondly, many of the subjects reported a high level of discomfort
while they were wearing the stockings.

Which highlights a problem: there's no current standard for how much pressure
a compression garment should apply. Similarly, relatively few studies have looked
at the garments' effects during exercise.

A numbers game

Share your experience

That was until a new study from Central Queensland University in Australia
set out to look for concrete benefits. Aaron Scanlan and his team measured the
effects of wearing lower-body compression garments in a cycling time trial.
Using traditional statistics, they found no evidence of a benefit in the categories
measured. Yet this isn't quite the end of the story.

"There's a question as to whether traditional statistics are adequate for sports
science research," says Scanlan. "Sometimes a minor improvement won't show statistical
significance, but a small change could be absolutely crucial to a top-level
athlete."

As a result, Scanlan also applied a technique called Magnitude-Based Inferences
to the data. Using this method he was able to show that power output and anaerobic
threshold were slightly improved when wearing compression garments and the efficiency
of the muscle oxygenation process was also marginally better. These findings
have persuaded Scanlan that compression garments should not be dismissed and
that further research is necessary.

Evidence for recovery benefits is equally circumstantial, but compelling. In
a 2007 study at Massey University in New Zealand researchers asked subjects
to record the soreness in their legs the day after completing a steady 10km
run, both with and without compression socks. When wearing the socks, two of
the 14 subjects reported soreness the following day; without the socks, that
rose to all but one.

"It's true that recovery responses with the use of compression garments have
been much more positive than performance responses," says Scanlan. "But the
perception of muscle soreness is largely measured by questionnaires, in which
the placebo effect could be at play.

"The only real practical advice I can give at the moment is to ignore the results
on the use of compression garments and try them out," he added. "If they feel
good to wear during cycling, then wear them during cycling, and if they feel
good during recovery, wear them during recovery."